The present invention relates to a process for testing transparent material webs, particularly flat, plate or sheet glass ribbons or the like for material defects, in which the glass ribbon or the like conveyed in its longitudinal direction is scanned with a laser-produced flying light spot over its width in a scanning plane at right angles to its conveying plane and direction, the forward and back scattering produced by the inclusions is in each case measured in a detection plane sloping with respect to the scanning plane, electrical signals being derived from the measured values obtained and processed for material defect identification. The invention also relates to an apparatus for testing transparent material webs, particularly flat, plate or sheet glass ribbons or the like for material defects, with a light spot source arranged on one side of the glass ribbon or the like conveyed in the longitudinal direction thereof for producing a laser-produced flying light spot scanning the glass ribbon over its width in a scanning plane at right angles to its conveying plane and direction, as well as detectors arranged on either side of the glass ribbon or the like for detecting the forward or back scattering produced by the inclusions in in each case a detection plane sloping with respect to the scanning plane.
In certain circumstances, nickel sulphide (NiS) inclusions in tempered glass plates can lead to spontaneous breakages (Glastechn. Ber, 50 (1977) No. 11, pp 296-300) leading to a not inconsiderable risk to people, particularly in the case of glass facades. In order to avoid the use of such faulty glass plates, it has hitherto been conventional practice to use a so-called heat-soak test, in which following tempering the glass plates undergo an appropriate heat treatment, so that the phase transition of the NiS-inclusions causing the breakages or shattering is forced beforehand. The glass plates which survive this test without damage can then be used for the glazing of buildings with a much greater shatterproof protection. However, the aforementioned selection process is unsatisfactory for obvious economic reasons.
British Pat. No. 13 38 611 already discloses a process and an apparatus of the aforementioned type for testing glass ribbons, in which glass ribbons removed e.g. from float glass plants are investigated for material defects. Fundamentally this known process makes it possible to detect NiS-inclusions, in the case of a corresponding highly sensitive setting, but does not make it possible to distinguish these from other glass defects, particularly glass stones. Other similarly functioning glass testing means of this type, such as those known e.g. from German Pat. No. 31 29 808, also permit in the case of a highly sensitive setting, the detection inter alia of NiS-inclusions, without being able to distinguish these from other glass defects and in particular glass stones, so that the aforementioned processes are not suitable for exclusively eliminating glass plates having NiS-inclusions and which are therefore defective, because in this case the said processes would also eliminate those plates having defects not leading to the aforementioned spontaneous breakages, so that an excessive amount of material would be discarded as waste.
Therefore the problem of the invention is to provide a process and an apparatus of the aforementioned type which, compared with the hitherto known processes and apparatuses, permit a better discrimination of the defects found according to type and size and which in particular offer the possibility of distinguishing NiS-inclusions from other glass defects.